Diamonds and other gemstones are commonly used both for cosmetic applications in the jewelry industry and for industrial applications, such as cutting, drilling, grinding, and polishing.
We will refer below mostly to diamonds, however, the discussion is the same for other gemstones made of other materials. Due in part to the increased demand for such applications and the relatively high price for even small sized diamonds, synthetic diamond industries are rapidly growing. Despite the growth in the synthetic diamond market, sales of natural diamonds have remained steady or have grown over the past 10 years. As such, there is a large market demand for both natural and synthetic diamonds.
In the jewelry industry, the value of a diamond, sapphire, etc., depends at least partially on its optical performance, or clarity. Diamonds that are absolutely clear are typically the most expensive and the most sought-after. However, most diamonds have internal imperfections, such as cracks, inclusions and vacant volumes that detract from the diamond's value and beauty. These defects reflect or absorb light incident on the defect's surface and are visible to the consumer. A crack has two surfaces that reflect light, and approximately 17% of the light incident on a crack is reflected due to the high refractive index of the diamond. Such defects reduce the value of a diamond significantly. These defects may also reduce a diamond's value in industrial applications too, including by increasing the risk of failure due to breaking along cracks or flaw lines.
It is therefore often necessary or desirable to improve the quality of a diamond or other gemstone by eliminating internal defects, and thereby improve a diamond's optical performance. Typically, inclusions inside diamonds are treated by drilling a hole to the defect with a laser and dissolving the inclused material with hot acids. This process leaves a vacant volume. Some diamond dealers fill cracks and vacant volumes with high refractive index glass to minimize the reflection and the visibility of these defects. However, diamonds having fillers are less valuable then diamonds without fillers. There are known chemical processes relied upon in the jewelry industry for improving a diamond's appearance. CVD has previously been used to grow single crystal diamonds. CVD involves feeding various amounts of gases into a chamber while providing the conditions necessary for carbon atoms in a gas to settle on a substrate in crystalline form. However, CVD diamond layer thickness may not be accurate and is frequently difficult to control.
Current efforts have been made to grow a single crystal diamond (outside of the high pressure furnace crystallization) using CVD technology. For example, the Carnegie Institute's Geophysical Laboratory can produce a 10 carat (2 g) single-crystal diamond rapidly (28 nm/s) by CVD, as well as a colorless single-crystal diamond. Growth of colorless diamonds up to 60 g (300 carats) is believed achievable using their method. (See http://www.scienceblog.com/cms/node/7908, which is incorporated herein by reference in its entirety.)
But despite the above mentioned methods, there remains a need for a relatively simple, repeatable, inexpensive and otherwise economical method for improving the quality of diamonds and other precious stones.